U.S. patent number 11,047,955 [Application Number 16/029,473] was granted by the patent office on 2021-06-29 for calibrating a radar antenna.
This patent grant is currently assigned to Lyft, Inc.. The grantee listed for this patent is Lyft, Inc.. Invention is credited to Farzad Cyrus Foroughi Abari, Romain Clement, Mayur Nitinbhai Shah.
United States Patent |
11,047,955 |
Abari , et al. |
June 29, 2021 |
Calibrating a radar antenna
Abstract
In one embodiment, a method includes causing a radar antenna to
transmit a plurality of radar signals at a plurality of sweep
angles and, for each of one or more the radar signals reflected
back to the radar antenna, calculating a radial-velocity component.
The method also includes identifying one of the radial-velocity
components, identifying one of the plurality of sweep angles
corresponding to the identified radial-velocity components, and
calculating an offset of an electrical boresight of the radar
antenna based at least in part on the identified sweep angle
corresponding to the identified radial-velocity component.
Inventors: |
Abari; Farzad Cyrus Foroughi
(San Bruno, CA), Clement; Romain (Campbell, CA), Shah;
Mayur Nitinbhai (Pleasanton, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Lyft, Inc. |
San Francisco |
CA |
US |
|
|
Assignee: |
Lyft, Inc. (San Francisco,
CA)
|
Family
ID: |
1000005648320 |
Appl.
No.: |
16/029,473 |
Filed: |
July 6, 2018 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20200011970 A1 |
Jan 9, 2020 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01S
7/4026 (20130101); G01S 7/403 (20210501) |
Current International
Class: |
G01S
7/40 (20060101) |
Field of
Search: |
;342/174 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Daniel De Zutter "Scattering by a Rotating Dielectric Sphere" in
IEEE Transactions on Antennas and Propagation, vol. AP-28, No. 5,
Sep. 1980 (Year: 1980). cited by examiner .
Ayoub Soltane, Guillaume Andrieu, Alain Reineix "Analytical Model
for the Assessment of Doppler Spectrum of Rotating Objects" in
Proc. of the 2017 International Symposium on Electromagnetic
Compatibility--EMC Europe 2017, Angers, France, Sep. 4-8, 2017
(Year: 2017). cited by examiner.
|
Primary Examiner: Magloire; Vladimir
Assistant Examiner: Syrkin; Alexander L.
Attorney, Agent or Firm: Baker Botts L.L.P.
Claims
The invention claimed is:
1. A method comprising, by a computing device: causing a radar
antenna to transmit radar signals at a plurality of sweep angles;
calculating a respective value of a radial-velocity component
corresponding to one or more reflected radar signals of the
transmitted radar signals reflected back to the radar antenna;
identifying one or more of the one or more radial-velocity
components based on the one or more respective values of the one or
more radial-velocity components; identifying a sweep angle of the
plurality of sweep angles corresponding to the one or more
identified radial-velocity components; calculating an offset
between an actual electrical boresight of the radar antenna based
at least in part on the identified sweep angle corresponding to the
one or more identified radial-velocity components and an expected
electrical boresight of the radar antenna; and causing the radar
antenna to be calibrated based on the calculated offset.
2. The method of claim 1, wherein causing the radar antenna to be
calibrated comprises causing the calculated offset to be accounted
for in future measurements by the radar antenna.
3. The method of claim 1, wherein causing the radar antenna to be
calibrated comprises causing an orientation of the radar antenna to
be changed based at least in part on the calculated offset.
4. The method of claim 1, wherein: the radar antenna transmits the
radar signals in one or more horizontal sweeps; and the calculated
offset of the actual electrical boresight of the radar antenna is
horizontal.
5. The method of claim 1, wherein: the radar antenna transmits the
radar signals in one or more vertical sweeps; and the calculated
offset of the actual electrical boresight of the radar antenna is
vertical.
6. The method of claim 1, wherein the reflected radar signals are
reflected from a plurality of locations on a substantially planar
surface moving at a substantially constant velocity relative to the
radar antenna.
7. The method of claim 1, wherein the reflected radar signals are
reflected from a plurality of locations on a surface of a sphere
rotating at a constant speed in front of the radar antenna.
8. The method of claim 1, wherein the radar antenna is located in
or on a vehicle.
9. The method of claim 8, wherein the vehicle is an autonomous
vehicle.
10. The method of claim 8, wherein the radar antenna is located: on
top of the vehicle; or on or in a bumper of the vehicle.
11. A system comprising: one or more processors; and one or more
computer-readable non-transitory storage media in communication
with the one or more processors, the one or more computer-readable
non-transitory storage media comprising instructions that, when
executed by the one or more processors, are configured to cause the
system to perform operations comprising: causing a radar antenna to
transmit radar signals at a plurality of sweep angles; calculating
a respective value of a radial-velocity component corresponding to
one or more reflected radar signals of the transmitted radar
signals reflected back to the radar antenna; identifying one or
more of the one or more radial-velocity components based on the one
or more respective values of the one or more radial-velocity
components; identifying a sweep angle of the plurality of sweep
angles corresponding to the one or more identified radial-velocity
components; calculating an offset between an actual electrical
boresight of the radar antenna based at least in part on the
identified sweep angle corresponding to the one or more identified
radial-velocity components and an expected electrical boresight of
the radar antenna; and causing the radar antenna to be calibrated
based on the calculated offset.
12. The system of claim 11, wherein causing the radar antenna to be
calibrated comprises causing the calculated offset to be accounted
for in future measurements by the radar antenna.
13. The system of claim 11, wherein causing the radar antenna to be
calibrated comprises causing an orientation of the radar antenna to
be changed based at least in part on the calculated offset.
14. The system of claim 11, wherein: the radar antenna transmits
the radar signals in one or more horizontal sweeps; and the
calculated offset of the actual electrical boresight of the radar
antenna is horizontal.
15. The system of claim 11, wherein: the radar antenna transmits
the radar signals in one or more vertical sweeps; and the
calculated offset of the actual electrical boresight of the radar
antenna is vertical.
16. The system of claim 11, wherein the reflected radar signals are
reflected from a plurality of locations on a substantially planar
surface moving at a substantially constant velocity relative to the
radar antenna.
17. One or more computer-readable non-transitory storage media
including instructions that, when executed by one or more
processors of a computing system, are configured to cause the one
or more processors to perform operations comprising: causing a
radar antenna to transmit radar signals at a plurality of sweep
angles; calculating a respective value of a radial-velocity
component corresponding to one or more reflected radar signals of
the transmitted radar signals reflected back to the radar antenna;
identifying one or more of the one or more radial-velocity
components based on the one or more respective values of the one or
more radial-velocity components; identifying a sweep angle of the
plurality of sweep angles corresponding to the one or more
identified radial-velocity components; calculating an offset
between an actual electrical boresight of the radar antenna based
at least in part on the identified sweep angle corresponding to the
one or more identified radial-velocity components and an expected
electrical boresight of the radar antenna; and causing the radar
antenna to be calibrated based on the calculated offset.
18. The one or more computer-readable non-transitory storage media
claim 17, wherein the reflected radar signals are reflected from a
plurality of locations on a substantially planar surface moving at
a substantially constant velocity relative to the radar
antenna.
19. The one or more computer-readable non-transitory storage media
claim 17, wherein the reflected radar signals are reflected from a
plurality of locations on a surface of a sphere rotating at a
constant speed in front of the radar antenna.
20. The method of claim 8, wherein the calculated offset
corresponds to the actual electrical boresight of the radar antenna
being misaligned with a central longitudinal axis of the
vehicle.
21. The method of claim 1, wherein the actual electrical boresight
of the radar antenna corresponds to an axis of maximum radiated
power of the radar antenna.
22. The method of claim 1, wherein one of the one or more
identified radial-velocity components is a maximum radial-velocity
component.
23. The method of claim 1, wherein identifying the sweep angle of
the plurality of sweep angles corresponding to the one or more
identified radial-velocity components comprises calculating a sweep
angle based on the one or more identified radial-velocity
components.
Description
BACKGROUND
A vehicle (such as an autonomous vehicle) for transporting humans
or goods may be equipped with a radar system used to determine the
locations and shapes of objects near the vehicle. The radar system
may include one more radar antennas. A radar antenna has an
electrical boresight that is the axis of maximum gain (or maximum
radiated power) of the radar antenna, and the radiation pattern of
the radar antenna may be symmetrical about its electrical
boresight. If the radar antenna is properly calibrated, then its
expected electrical boresight will be aligned with its actual
electrical boresight. The expected electrical boresight of the
radar antenna is the electrical boresight that the radar system
expects the radar antenna to have, and the actual electrical
boresight of the radar antenna is the electrical boresight that the
radar antenna actually has. If the radar antenna is not properly
calibrated, then its expected electrical boresight may differ from
its actual electrical boresight, which may make the radar system
less accurate.
The orientation of the radar antenna may, at least in part,
determine its electrical boresight. The orientation of a radar
antenna on a vehicle may change over time, e.g., due to collisions,
driving over potholes, or normal vibrations that occur when
driving. As the orientation of the radar antenna changes, the
actual electrical boresight of the radar antenna may deviate from
its expected electrical boresight and the vehicle's radar system
may become less accurate. To address this, the radar antenna may
periodically be recalibrated. Traditional calibration methods
involve placing the vehicle inside an anechoic chamber with a
reflective trihedral in line with the expected electrical boresight
of the radar antenna on the vehicle.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A illustrates an example vehicle with an example radar
antenna that has an expected electrical boresight horizontally
aligned with its actual electrical boresight.
FIG. 1B illustrates an example vehicle with an example radar
antenna that has an expected electrical boresight that differs
horizontally from its actual electrical boresight.
FIG. 2 illustrates an example system for calibrating a radar
antenna on a vehicle in an open area.
FIG. 3 illustrates the example system of FIG. 2 from a top-down
view.
FIG. 4 illustrates an example characteristic curve of radial
velocities observed by a radar antenna through a sweep range.
FIG. 5 illustrates another example characteristic curve of radial
velocities observed by a radar antenna through a sweep range.
FIG. 6 illustrates another example system for calibrating a radar
antenna on a vehicle using a rotating sphere.
FIG. 7 illustrates the example system of FIG. 6 from a top-down
view.
FIG. 8 illustrates an example method for calibrating a radar
antenna on a vehicle.
FIG. 9 illustrates an example computing system.
DESCRIPTION OF EXAMPLE EMBODIMENTS
In the following description, various embodiments are described.
For purposes of explanation, specific configurations and details
are set forth in order to provide a thorough understanding of the
embodiments. However, it will also be apparent to one skilled in
the art that the embodiments may be practiced without the specific
details. Furthermore, well-known features may be omitted or
simplified in order not to obscure the embodiment being described.
In addition, the embodiments disclosed herein are only examples,
and the scope of this disclosure is not limited to them. Particular
embodiments may include all, some, or none of the components,
elements, features, functions, operations, or steps of the
embodiments disclosed above. Embodiments according to the invention
are in particular disclosed in the attached claims directed to a
method, a storage medium, a system and a computer program product,
wherein any feature mentioned in one claim category, e.g., method,
can be claimed in another claim category, e.g., system, as well.
The dependencies or references back in the attached claims are
chosen for formal reasons only. However, any subject matter
resulting from a deliberate reference back to any previous claims
(in particular multiple dependencies) can be claimed as well, so
that any combination of claims and the features thereof are
disclosed and can be claimed regardless of the dependencies chosen
in the attached claims. The subject matter which can be claimed
comprises not only the combinations of features as set out in the
attached claims but also any other combination of features in the
claims, wherein each feature mentioned in the claims can be
combined with any other feature or combination of other features in
the claims. Furthermore, any of the embodiments and features
described or depicted herein can be claimed in a separate claim or
in any combination with any embodiment or feature described or
depicted herein or with any of the features of the attached
claims.
The electrical boresight of a radar antenna is the axis of maximum
gain (or maximum radiated power) of the radar antenna, and the
radiation pattern of the radar antenna may be symmetrical about its
electrical boresight. Herein, reference to a radar antenna may
encompass one or more devices for transmitting or receiving
electromagnetic waves, where appropriate. For example, where
appropriate, reference to a radar antenna may indicate a single
device for transmitting electromagnetic waves; a single device for
receiving electromagnetic waves; a single device for transmitting
and receiving electromagnetic waves; a combination of multiple
devices for transmitting electromagnetic waves; a combination of
multiple devices for receiving electromagnetic waves; or a
combination of multiple devices for receiving and electromagnetic
waves. A radar antenna may be part of a radar system (such as an
automotive imaging radar system), which may include which may
include hardware, software, or both for controlling the radar
antenna and for processing and analyzing output from the radar
antenna. Reference herein to a radar antenna may encompass a radar
system that the radar antenna is a part of, and vice versa, where
appropriate.
If the radar antenna is calibrated properly, the expected
electrical boresight of the radar antenna will be aligned with the
actual electrical boresight of the radar antenna. Traditional
calibration methods involve placing the radar antenna inside an
anechoic chamber with a reflective trihedral in line with the
expected electrical boresight of the radar antenna. If the actual
electrical boresight of the radar antenna is aligned with the
expected electrical boresight of the radar antenna, then the
trihedral will reflect the radar signal from radar antenna back to
the radar antenna. On the other hand, if the actual electrical
boresight is out of alignment with the expected electrical
boresight, then little or none of the radar signal will be
reflected back to the radar antenna. The orientation of the radar
antenna may be changed or the radar signal from the radar antenna
may otherwise be redirected until it is reflected back to the radar
antenna by the trihedral, indicating that the actual and expected
electrical boresights of the radar antenna are aligned with each
other. In addition or as an alternative, the trihedral may be moved
relative to the radar antenna until it reflects the radar signal
back to the radar antenna. When the radar signal is reflected back
to the radar antenna by the trihedral, the actual electrical
boresight of the radar antenna may be recorded and its offset from
the expected electrical boresight of the radar antenna calculated.
The radar antenna may then be recalibrated. Traditional calibration
methods are burdensome and expensive. In particular embodiments, to
reduce the cost and time necessary to calibrate a radar antenna, a
radar antenna may be calibrated using an open area or rotating
sphere. FIGS. 2 and 3 illustrate example calibration using an open
area. FIGS. 6 and 7 illustrate example calibration using a rotating
sphere.
FIG. 1A illustrates an example vehicle with an example radar
antenna that has an expected electrical boresight horizontally
aligned with its actual electrical boresight. In the example of
FIG. 1A, vehicle 100 (which may in particular embodiments be an
autonomous vehicle) is equipped with an automotive imaging radar
system that includes radar antenna 110. Although radar antenna 110
is described and illustrated as being in front of vehicle 100, this
disclosure contemplates radar antenna 110 (or one or more
components of radar antenna 110) being on or in, or integrated into
any suitable location on or in, vehicle 100. For example, one or
more components of radar antenna 110 may be located on top of
vehicle 100 (as illustrated in FIG. 2) or elsewhere in or on
vehicle 100. Radar antenna 110 transmits a radar signal that has a
main lobe 120 and side lobes 130. Main lobe 120 is split by actual
electrical boresight 121 of radar antenna 110. Actual electrical
boresight 121 is horizontally aligned with expected electrical
boresight 122 of radar antenna 110. Thus, horizontal measurements
by radar antenna 110 may be more accurate. By contrast, FIG. 1B
illustrates an example vehicle with an example radar antenna that
has an expected electrical boresight that differs horizontally from
its actual electrical boresight. In the example of FIG. 1B, actual
electrical boresight 121 is horizontally offset from expected
electrical boresight 122 by offset 123. Offset 123 may have
resulted from radar antenna 110 becoming damaged, moved, or
otherwise affected by one or more collisions, driving on rough
roads (e.g., driving over potholes), or through normal vibrations
of vehicle 110 that occur when driving. As a result, horizontal
measurements by radar antenna 110 in FIG. 1B may be less accurate.
For example, if offset 123 is 5.degree. to the right, a radar
system of vehicle 110 may determine, based on measurements by radar
antenna 110, that an object is located directly in front of vehicle
100 when in reality the object is located 5.degree. to the right of
a center line of the vehicle. Offset 123 may thus cause vehicle 100
to miscalculate the locations of objects. However, if the amount of
offset 123 between actual electrical boresight 121 and expected
electrical boresight 122 is known by the radar system of vehicle
100, the radar system may be able to correct for offset 123 when
calculating the location of an object based on measurements by
radar antenna 110. Particular embodiments facilitate the
determination of the amount of this offset to enable the radar
system to correct for it.
FIG. 2 illustrates an example system for calibrating a radar
antenna 110 on a vehicle 100 in an open area. Although radar
antenna 110 is described and illustrated as being on top of vehicle
100 in the example of FIG. 2, this disclosure contemplates radar
antenna 110 (or one or more components of radar antenna 110) being
on or in, or integrated into any suitable location on or in,
vehicle 100. For example, one or more components of radar antenna
110 may be located on or in a front bumper of vehicle 100 (as
illustrated in FIGS. 1A and 1B) or elsewhere in or on vehicle 100.
In the example of FIG. 2, to calibrate radar antenna 110, vehicle
100 drives forward at a substantially constant velocity in a
substantially straight line on a substantially flat surface while
radar antenna 110 transmits radar signals 220 in front of vehicle
100 at a substantially constant elevation angle 4), indicated by
reference number 221, through a sweep range 223 (illustrated in the
top-down view of FIG. 3). During this process, radar signals 220
are reflected back to radar antenna 110 from locations 230, which
collectively form a circular arc (also illustrated in the
top-down-view of FIG. 3) in front of vehicle 100 on the surface
that vehicle 100 is driving on. As an example and not by way of
limitation, elevation angle 221 may be -5.degree. and the radial
distance between radar antenna 110 and locations 230 may be 20
meters. Elevation angle 221 may depend on the size of the open area
available to vehicle 110 during the calibration process. For
example, an elevation angle of -5.degree. may be used in a larger
open area and an elevation angle of -15.degree. may be used in a
smaller open area. In particular embodiments, a smaller elevation
angle 221 may provide more accurate results. In particular
embodiments, the radar system of vehicle 100 (or one or more other
systems or components of vehicle 100) may be able to account for
one or more changes in the velocity of vehicle 100, curves in the
path driven by vehicle 100, unevenness in the surface that vehicle
100 is driving on, or changes in elevation angle 221 during the
calibration process, so that vehicle 100 does not necessarily have
to drive at a substantially constant velocity in a substantially
straight line on a substantially flat surface. For example, if
vehicle 100 does not drive in a substantially straight line, the
orientation of vehicle 100 may be monitored with an inertial sensor
or other suitable internal navigation system (INS) sensor and then
accounted for (as described below).
Radar antenna 110 may transmit radar signals 220 at different
sweep, or azimuth, angles .theta. through sweep range 223. The
sweep angles .theta. may range from a negative value to a positive
value, for example from -55.degree. to +55.degree., with 0.degree.
being aligned with a central longitudinal 240 axis of vehicle 100
(illustrated in the top-down view of FIG. 3). Radar antenna 110 may
transmit a radar signal 220 at every degree within the sweep range,
e.g., .theta..sub.i=-55.degree., -54.degree., -53.degree., . . . ,
+54.degree., +55.degree.. Alternatively, radar antenna 110 may
transmit a radar signal 220 at other predetermined intervals, such
as every other degree, e.g., .theta..sub.i=-55.degree.,
-53.degree., -51.degree., . . . , +53.degree., +55.degree., or any
other suitable interval(s). Doppler shifts in radar signals 220
reflected back to radar antenna 110 from locations 230 may be
measured by the radar system of vehicle 100 to determine the
radial-velocity component .nu..sub.r of each location 230 relative
to radar antenna 110 (which is moving forward with vehicle 100). If
vehicle 100 is moving in a straight line at a speed of .nu..sub.0
meters per second and radar antenna 110 is properly calibrated in
elevation, then the radial-velocity component .nu..sub.r of a
location 230 relative to radar antenna 110 will be .nu..sub.r
(.theta..sub.i,.PHI.)=.nu..sub.0 cos(.theta..sub.i) cos(.PHI.) for
sweep angle .theta..sub.i corresponding to that location 230 and
for elevation angle .PHI.. A cosine function may be fit to the
resulting characteristic curve through sweep range 223 that an
azimuthal beam offset 123, if any, may be calculated from, as
described below with reference to FIGS. 4 and 5. In particular
embodiments, this calibration process may last a relatively short
duration of time, such as, for example, between 0.001 seconds and
0.5 seconds.
FIG. 3 illustrates the example calibration system of FIG. 2 from a
top-down view. In the example of FIG. 3, sweep range 223 extends
from location 230A to location 230M. Although FIG. 3 shows a
particular number of particular locations 230, this disclosure
contemplates any suitable number of any suitable locations. As an
example and not by way of limitation, radar antenna may transmit
radar signals 220 at 60 different sweep angles .theta. through
sweep range 223 and radar signals 220 may be reflected back to
radar antenna 110 from 60 different locations 230 on the ground.
When the sweep angle .theta. is at the extreme positions (e.g.
.theta..sub.i=-55.degree. or +55.degree.) and radar signals 220 are
being reflected back to radar antenna 110 from leftmost and
rightmost locations 230 (e.g. locations 230A and 230M), the
radial-velocity component observed by radar antenna 110 will be at
a minimum (e.g. cos.+-.55.degree.=0.57 and cos 0.degree.=1). If the
expected electrical boresight of radar antenna 110 is horizontally
aligned with a central longitudinal axis 240 of vehicle 100 and
radar antenna 110 is properly horizontally oriented, then the
radial-velocity component observed by radar antenna 110 will be
greatest at a sweep angle of 0.degree. from central longitudinal
axis 240 of vehicle 100. However, if radar antenna 110 is not
properly horizontally oriented, then the radial-velocity component
observed by radar antenna 110 will be greatest at a sweep angle
other than 0.degree. from central longitudinal axis 240 of vehicle
100. The sweep angle with the greatest radial-velocity component
observed by radar antenna 110 may be determined by plotting the
radial-velocity components observed by radar antenna 110 through
sweep range 223 (as illustrated in FIGS. 4 and 5), which may
indicate an offset 123 (if any) between the expected electrical
boresight and the actual electrical boresight of radar antenna 110.
Although this disclosure describes and illustrates determining
particular offsets 123 between particular actual and expected
electrical boresights, this disclosure contemplates determining any
suitable offset 123 between any suitable actual and expected
electrical boresights. Moreover, this disclosure contemplates
determining any suitable number and types of offsets 123. For
example, in particular embodiments, in addition or as an
alternative to a horizontal offset 123 between the actual and
expected electrical boresights of a radar antenna 110 being
determined, a vertical offset 123 between the actual and expected
electrical boresights of radar antenna 110 may be determined by
"rolling" radar antenna 110 onto its side (e.g. rotating it
90.degree. to the left or right) and then sweeping radar antenna
110 through sweep range 123 at elevation angle 221 (simulating a
vertical sweep of radar antenna 110) as it transmits radar signals
220 and performing steps similar to those described and illustrated
herein for determining a horizontal offset 123.
In particular embodiments, vehicle 100 does not necessarily have to
drive in a substantially straight line. The orientation of vehicle
100, .theta..sub.I, may be monitored with an inertial sensor or
other suitable INS sensor. If vehicle 100 is moving forward at a
speed of .nu..sub.0 meters per second while its orientation is
monitored and radar antenna 110 is properly calibrated in
elevation, then the radial-velocity component .nu..sub.r of a
location 230 relative to radar antenna 110 for sweep angle
.theta..sub.i corresponding to that location 230 and for elevation
angle .PHI. may be calculated as follows:
.nu..sub.r(.theta..sub.i,.theta..sub.I,.PHI.)=.nu..sub.0
cos(.PHI.)cos(.theta..sub.i+.theta..sub.I)
.nu..sub.r(.theta..sub.i,.theta..sub.I,.PHI.)=.nu..sub.0
cos(.PHI.)[cos(.theta..sub.i)cos(.theta..sub.I)+sin(.theta..sub.i)sin(.th-
eta..sub.I)] In this example, the known orientation of the vehicle
.theta..sub.I may be subtracted from the measurements to find the
characteristic curve with respect to azimuth.
After an offset 123 (if any) between the expected electrical
boresight and the actual electrical boresight of radar antenna 110
is determined, radar antenna 110 may then be calibrated. Radar
antenna 110 may be moved or its orientation otherwise changed to
reduce or eliminate offset 123. For example, if offset 123 is
5.degree. to the right, then radar antenna 110 may be reoriented to
move its actual electrical boresight moves 5.degree. to the left.
In addition or as an alternative, all or some of offset 123 may be
corrected for or otherwise taken into account in calculations
performed based on measurements by radar antenna 110. For example,
if offset 123 is 5.degree. to the right, then the radar system of
vehicle 110 may adjust 5.degree. to the left measurements by radar
antenna 110 when performing calculations based on those
measurements. Although this disclosure describes and illustrates
particular steps for calibrating a radar antenna 110 after
determining an offset 123, this disclosure contemplates any
suitable steps for calibrating radar antenna 110 after determining
offset 123. In particular embodiments (e.g. when the radar antenna
110 is part of a radar system of an autonomous vehicle), this
calibration of radar antenna 110 may be initiated and completed
entirely in the field, automatically and without user input. This
may include transmitting radar signals 220 through a sweep range
223, calculating radial-velocity components for radar signals 220
reflected back to radar antenna 110, identifying a maximum
radial-velocity component (or a zero radial-velocity component as
described below with reference to FIGS. 6 and 7) and its
corresponding sweep angle, calculating an offset 123 (if any) based
on the maximum radial-velocity components (or zero radial-velocity
component), and calibrating radar antenna 110 based on offset 123,
entirely in the field, automatically and without user input.
FIG. 4 illustrates an example characteristic curve of radial
velocities observed through a sweep range 223 by a radar antenna
110 on a vehicle 100 in the system of FIGS. 2 and 3. In the example
of FIG. 4, the maximum observed radial velocity occurs at point
411, which corresponds to a sweep angle .theta. of 0.degree. from a
central longitudinal 240 axis of vehicle 100. This indicates that
the actual electrical boresight of radar antenna 110 is
horizontally aligned with central longitudinal axis 240 of vehicle
100. If the electrical boresight of radar antenna 110 expected by
the radar system of vehicle 100 is also 0.degree. from central
longitudinal 240 axis of vehicle 100, then this also indicates that
radar antenna 110 is properly horizontally calibrated.
FIG. 5 illustrates another example characteristic curve of radial
velocities observed through a sweep range 223 by a radar antenna
110 on a vehicle 100 in the system of FIGS. 2 and 3. In the example
of FIG. 5, the maximum observed radial velocity occurs at point
511, which corresponds to a sweep angle .theta. of approximately
+10.degree. from a central longitudinal axis 240 of vehicle 100.
This indicates that the actual electrical boresight of radar
antenna 110 is offset from central longitudinal axis 240 of vehicle
100 by +10.degree.. If the electrical boresight of radar antenna
110 expected by the radar system of vehicle 100 is 0.degree. from
central longitudinal 240 axis of vehicle 100, then this also
indicates that radar antenna 110 is not properly horizontally
calibrated and the radar system should take into account an offset
123 of +10.degree. when, e.g., calculating the location of an
object based on measurements by radar antenna 110. In particular
embodiments, this may be accomplished by subtracting 10.degree.
from the horizontal bearing of a measurement by radar antenna
110.
FIG. 6 illustrates an example system for calibrating a radar
antenna on a vehicle using a rotating sphere. This system uses a
rotating sphere 620, instead of the ground or other surface that
vehicle 100 is driving on, as the reflective surface. Sphere 620
may have a diameter of one to three feet. Although sphere 620 is
described and illustrated as having particular dimensions, this
disclosure contemplates sphere 620 having any suitable dimensions.
In the example of FIG. 6, to calibrate radar antenna 110, sphere
620 is placed in front of radar antenna 110 at a suitable distance
(e.g. 20 feet), with the center of sphere 620 aligned with the
expected electrical boresight of radar antenna 110. The distance
between radar antenna 110 and sphere 620 may depend on the bearing
resolution of radar antenna 110. As an example and not by way of
limitation, a distance of 20 feet may be suitable if radar antenna
110 has a bearing resolution of less than 2.degree. horizontally
and vertically (i.e. with respect to azimuth and elevation). With
the center of sphere 620 vertically and horizontally aligned with
the expected electrical boresight of radar antenna radar 110,
sphere 620 is rotated at a substantially constant speed. In
particular embodiments, sphere 620 may be rotated at a speed of
200, 500, or 1,000 revolutions per minute (RPM). This disclosure
contemplates any suitable sphere 620 rotating at any suitable
speed. Vehicle 100 remains stationary during this calibration
process. As sphere 620 rotates, radar antenna 110 transmits radar
signals 220 while sweeping horizontally across the front of sphere
620 through a sweep range 223. During this process, radar signals
220 are reflected back to radar antenna 110 from locations 621 on
sphere 620. Doppler shifts in radar signals 220 reflected back to
radar antenna 110 from locations 621 may be measured by the radar
system of vehicle 100 to determine the radial-velocity component of
each location 621 relative to radar antenna 110.
FIG. 7 illustrates a top-down view of the example calibration
system of FIG. 6. In the example of FIG. 7, sweep range 223 extends
from location 621A to location 621I across the front of sphere 620.
When the sweep angle is at the extreme positions (e.g. location
621A or 621I), the radial-velocity component observed by radar
antenna 110 will be at a maximum (either positive or negative). If
the actual electrical boresight of radar antenna 110 is
horizontally aligned with the center of sphere 620 (which is
horizontally aligned with the expected electrical boresight of
radar antenna 110), then the radial-velocity component observed by
radar antenna 110 will be zero at a sweep angle of 0.degree.,
indicating that radar antenna 110 is properly calibrated. However,
if the actual electrical boresight of radar antenna 110 is not
horizontally aligned with the center of sphere 620, then the
radial-velocity component observed by radar antenna 110 will be at
zero at a sweep angle other than 0.degree., indicating that radar
antenna 110 is not properly calibrated. The sweep angle with a
radial-velocity component of zero, as observed by radar antenna
110, may be determined by plotting the radial-velocity components
observed by radar antenna 110 through sweep range 223, which may in
turn indicate the offset between the expected electrical boresight
and the actual electrical boresight of radar antenna 110.
As an example and not by way of limitation, sphere 620 may spin
counter-clockwise at a fixed speed and radar antenna 110 may sweep
from left to right (e.g. it may start at location 621A and sweep
toward location 621I). At the leftmost location on sphere 620 (e.g.
location 621A), the tangential velocity of the surface of sphere
620 may point substantially toward radar antenna 110 and the radar
signal 220 reflected back to radar antenna 110 may, due to the
Doppler effect, have a frequency that is a positive maximum of all
radar signals 220 reflected back to radar antenna 110 from sphere
620. The surface of sphere 620 at location 621A is traveling
directly toward radar antenna 110, and the Doppler shift caused by
the tangential velocity of the surface of sphere 620 will cause the
frequency of the radar signal 220 reflected back to radar antenna
110 from location 621A to be higher than from all other locations
621 on sphere 620. As radar antenna 110 sweeps horizontally across
the front of sphere 620, starting at location 621A and proceeding
toward location 621I, the tangential velocity pointing toward radar
antenna 110 will decrease, which will cause the Doppler shift, and
the frequency of the radar signals 220 reflected back to radar
antenna 110, to decrease. At the center of sphere 620 (e.g.
location 621E), the tangential velocity of the surface of sphere
620 will be perpendicular to the actual electrical boresight of
radar antenna 110 (if radar antenna 110 is properly horizontally
calibrated), and no Doppler shift will be observed at that
location. As radar antenna 110 sweeps past the center of sphere
620, onto the side of sphere 620 that is spinning away from radar
antenna 110 (at locations 621E-621I), the Doppler shift may
decrease the frequency of radar signals 220 reflected back to radar
antenna 110. The radar system of vehicle 100 may determine the
sweep angle with no observed Doppler shift and thus determine the
horizontal component of the actual electrical boresight of radar
antenna 110.
Once the horizontal component of the actual electrical boresight is
determined, it may be desirable to determine the vertical component
the actual electrical boresight. As described above, this may be
done by rotating the radar antenna 90.degree. and applying the same
procedures as discussed herein. With the radar antenna 110 rotated
90.degree., the elevation angle .PHI. is the angle that changes
instead of the sweep angle .theta.. This way, if the system uses
the first calibration method, the vehicle can still drive in an
open area and use the driving surface as the reflective surface. If
the system uses the second calibration method, the radar antenna
may still use a sphere that is spinning horizontally (e.g.
counter-clockwise) instead of vertically.
FIG. 8 illustrates an example method 800 for calibrating a radar
antenna 110 on a vehicle 100 (which may be an autonomous vehicle).
The method may begin at step 810, where a computer system on board
or otherwise associated with vehicle 100 (and may be remote from
vehicle 100) causes radar antenna 110 on vehicle 100 to transmit
multiple radar signals at multiple different sweep angles
.theta..sub.i and at a substantially constant elevation angle
.PHI..sub.0 while vehicle 100 is driving in a substantially
straight line at a substantially constant velocity .nu..sub.0. At
step 820, after return radar signals are received at radar antenna
110, the computer system calculates multiple radial velocity
components .nu..sub.r for the return radar signals. At step 830,
the computer system identifies a maximum radial velocity component
of the radial velocity components. At step 840, the computer system
determines that the sweep angle .theta..sub.i corresponding to the
maximum radial velocity component indicates a horizontal component
of the actual electrical boresight of the radar antenna. At step
850, the computer system causes radar antenna 110 to be calibrated
based on the sweep angle .theta..sub.i corresponding to the maximum
radial velocity component, which in particular embodiments may be
carried out autonomously by radar antenna 110, possibly facilitated
by other devices on vehicle 110, at which point the method ends.
Particular embodiments may repeat one or more steps of the method
of FIG. 8, where appropriate. Although this disclosure describes
and illustrates particular steps of the method of FIG. 8 as
occurring in a particular order, this disclosure contemplates any
suitable steps of the method of FIG. 8 occurring in any suitable
order. Moreover, although this disclosure describes and illustrates
an example method for calibrating a radar antenna 110 on a vehicle
100 as including the particular steps of the method of FIG. 8, this
disclosure contemplates any suitable method for calibrating a radar
antenna 110 on a vehicle 100 as including any suitable steps, which
may include all, some, or none of the steps of the method of FIG.
8, where appropriate. Furthermore, although this disclosure
describes and illustrates particular components, devices, or
systems carrying out particular steps of the method of FIG. 8, this
disclosure contemplates any suitable combination of any suitable
components, devices, or systems carrying out any suitable steps of
the method of FIG. 8.
FIG. 9 illustrates an example computer system 900. In particular
embodiments, one or more computer systems 900 perform one or more
steps of one or more methods described or illustrated herein. In
particular embodiments, one or more computer systems 900 provide
the functionalities described or illustrated herein. In particular
embodiments, software running on one or more computer systems 900
performs one or more steps of one or more methods described or
illustrated herein or provides the functionalities described or
illustrated herein. Particular embodiments include one or more
portions of one or more computer systems 900. Herein, a reference
to a computer system may encompass a computing device, and vice
versa, where appropriate. Moreover, a reference to a computer
system may encompass one or more computer systems, where
appropriate.
This disclosure contemplates any suitable number of computer
systems 900. This disclosure contemplates computer system 900
taking any suitable physical form. As example and not by way of
limitation, computer system 900 may be an embedded computer system,
a system-on-chip (SOC), a single-board computer system (SBC) (such
as, for example, a computer-on-module (COM) or system-on-module
(SOM)), a desktop computer system, a laptop or notebook computer
system, an interactive kiosk, a mainframe, a mesh of computer
systems, a mobile telephone, a personal digital assistant (PDA), a
server, a tablet computer system, an augmented/virtual reality
device, or a combination of two or more of these. Where
appropriate, computer system 900 may include one or more computer
systems 900; be unitary or distributed; span multiple locations;
span multiple machines; span multiple data centers; or reside in a
cloud, which may include one or more cloud components in one or
more networks. Where appropriate, one or more computer systems 900
may perform without substantial spatial or temporal limitation one
or more steps of one or more methods described or illustrated
herein. As an example and not by way of limitation, one or more
computer systems 900 may perform in real time or in batch mode one
or more steps of one or more methods described or illustrated
herein. One or more computer systems 900 may perform at different
times or at different locations one or more steps of one or more
methods described or illustrated herein, where appropriate.
In particular embodiments, computer system 900 includes a processor
902, memory 904, storage 906, an input/output (I/O) interface 908,
a communication interface 910, and a bus 912. Although this
disclosure describes and illustrates a particular computer system
having a particular number of particular components in a particular
arrangement, this disclosure contemplates any suitable computer
system having any suitable number of any suitable components in any
suitable arrangement.
In particular embodiments, processor 902 includes hardware for
executing instructions, such as those making up a computer program.
As an example and not by way of limitation, to execute
instructions, processor 902 may retrieve (or fetch) the
instructions from an internal register, an internal cache, memory
904, or storage 906; decode and execute them; and then write one or
more results to an internal register, an internal cache, memory
904, or storage 906. In particular embodiments, processor 902 may
include one or more internal caches for data, instructions, or
addresses. This disclosure contemplates processor 902 including any
suitable number of any suitable internal caches, where appropriate.
As an example and not by way of limitation, processor 902 may
include one or more instruction caches, one or more data caches,
and one or more translation lookaside buffers (TLBs). Instructions
in the instruction caches may be copies of instructions in memory
904 or storage 906, and the instruction caches may speed up
retrieval of those instructions by processor 902. Data in the data
caches may be copies of data in memory 904 or storage 906 that are
to be operated on by computer instructions; the results of previous
instructions executed by processor 902 that are accessible to
subsequent instructions or for writing to memory 904 or storage
906; or any other suitable data. The data caches may speed up read
or write operations by processor 902. The TLBs may speed up
virtual-address translation for processor 902. In particular
embodiments, processor 902 may include one or more internal
registers for data, instructions, or addresses. This disclosure
contemplates processor 902 including any suitable number of any
suitable internal registers, where appropriate. Where appropriate,
processor 902 may include one or more arithmetic logic units
(ALUs), be a multi-core processor, or include one or more
processors 902. Although this disclosure describes and illustrates
a particular processor, this disclosure contemplates any suitable
processor.
In particular embodiments, memory 904 includes main memory for
storing instructions for processor 902 to execute or data for
processor 902 to operate on. As an example and not by way of
limitation, computer system 900 may load instructions from storage
906 or another source (such as another computer system 900) to
memory 904. Processor 902 may then load the instructions from
memory 904 to an internal register or internal cache. To execute
the instructions, processor 902 may retrieve the instructions from
the internal register or internal cache and decode them. During or
after execution of the instructions, processor 902 may write one or
more results (which may be intermediate or final results) to the
internal register or internal cache. Processor 902 may then write
one or more of those results to memory 904. In particular
embodiments, processor 902 executes only instructions in one or
more internal registers or internal caches or in memory 904 (as
opposed to storage 906 or elsewhere) and operates only on data in
one or more internal registers or internal caches or in memory 904
(as opposed to storage 906 or elsewhere). One or more memory buses
(which may each include an address bus and a data bus) may couple
processor 902 to memory 904. Bus 912 may include one or more memory
buses, as described in further detail below. In particular
embodiments, one or more memory management units (MMUs) reside
between processor 902 and memory 904 and facilitate accesses to
memory 904 requested by processor 902. In particular embodiments,
memory 904 includes random access memory (RAM). This RAM may be
volatile memory, where appropriate. Where appropriate, this RAM may
be dynamic RAM (DRAM) or static RAM (SRAM). Moreover, where
appropriate, this RAM may be single-ported or multi-ported RAM.
This disclosure contemplates any suitable RAM. Memory 904 may
include one or more memories 904, where appropriate. Although this
disclosure describes and illustrates particular memory, this
disclosure contemplates any suitable memory.
In particular embodiments, storage 906 includes mass storage for
data or instructions. As an example and not by way of limitation,
storage 906 may include a hard disk drive (HDD), a floppy disk
drive, flash memory, an optical disc, a magneto-optical disc,
magnetic tape, or a Universal Serial Bus (USB) drive or a
combination of two or more of these. Storage 906 may include
removable or non-removable (or fixed) media, where appropriate.
Storage 906 may be internal or external to computer system 900,
where appropriate. In particular embodiments, storage 906 is
non-volatile, solid-state memory. In particular embodiments,
storage 906 includes read-only memory (ROM). Where appropriate,
this ROM may be mask-programmed ROM, programmable ROM (PROM),
erasable PROM (EPROM), electrically erasable PROM (EEPROM),
electrically alterable ROM (EAROM), or flash memory or a
combination of two or more of these. This disclosure contemplates
mass storage 906 taking any suitable physical form. Storage 906 may
include one or more storage control units facilitating
communication between processor 902 and storage 906, where
appropriate. Where appropriate, storage 906 may include one or more
storages 906. Although this disclosure describes and illustrates
particular storage, this disclosure contemplates any suitable
storage.
In particular embodiments, I/O interface 908 includes hardware,
software, or both, providing one or more interfaces for
communication between computer system 900 and one or more I/O
devices. Computer system 900 may include one or more of these I/O
devices, where appropriate. One or more of these I/O devices may
enable communication between a person and computer system 900. As
an example and not by way of limitation, an I/O device may include
a keyboard, keypad, microphone, monitor, mouse, printer, scanner,
speaker, still camera, stylus, tablet, touch screen, trackball,
video camera, another suitable I/O device or a combination of two
or more of these. An I/O device may include one or more sensors.
This disclosure contemplates any suitable I/O devices and any
suitable I/O interfaces 808 for them. Where appropriate, I/O
interface 908 may include one or more device or software drivers
enabling processor 902 to drive one or more of these I/O devices.
I/O interface 908 may include one or more I/O interfaces 908, where
appropriate. Although this disclosure describes and illustrates a
particular I/O interface, this disclosure contemplates any suitable
I/O interface.
In particular embodiments, communication interface 910 includes
hardware, software, or both providing one or more interfaces for
communication (such as, for example, packet-based communication)
between computer system 900 and one or more other computer systems
900 or one or more networks. As an example and not by way of
limitation, communication interface 910 may include a network
interface controller (NIC) or network adapter for communicating
with an Ethernet or any other wire-based network or a wireless NIC
(WNIC) or wireless adapter for communicating with a wireless
network, such as a WI-FI network. This disclosure contemplates any
suitable network and any suitable communication interface 910 for
it. As an example and not by way of limitation, computer system 900
may communicate with an ad hoc network, a personal area network
(PAN), a local area network (LAN), a wide area network (WAN), a
metropolitan area network (MAN), or one or more portions of the
Internet or a combination of two or more of these. One or more
portions of one or more of these networks may be wired or wireless.
As an example, computer system 900 may communicate with a wireless
PAN (WPAN) (such as, for example, a Bluetooth WPAN), a WI-FI
network, a WI-MAX network, a cellular telephone network (such as,
for example, a Global System for Mobile Communications (GSM)
network), or any other suitable wireless network or a combination
of two or more of these. Computer system 900 may include any
suitable communication interface 910 for any of these networks,
where appropriate. Communication interface 910 may include one or
more communication interfaces 910, where appropriate. Although this
disclosure describes and illustrates a particular communication
interface, this disclosure contemplates any suitable communication
interface.
In particular embodiments, bus 912 includes hardware, software, or
both coupling components of computer system 900 to each other. As
an example and not by way of limitation, bus 912 may include an
Accelerated Graphics Port (AGP) or any other graphics bus, an
Enhanced Industry Standard Architecture (EISA) bus, a front-side
bus (FSB), a HYPERTRANSPORT (HT) interconnect, an Industry Standard
Architecture (ISA) bus, an INFINIBAND interconnect, a low-pin-count
(LPC) bus, a memory bus, a Micro Channel Architecture (MCA) bus, a
Peripheral Component Interconnect (PCI) bus, a PCI-Express (PCIe)
bus, a serial advanced technology attachment (SATA) bus, a Video
Electronics Standards Association local (VLB) bus, or another
suitable bus or a combination of two or more of these. Bus 912 may
include one or more buses 912, where appropriate. Although this
disclosure describes and illustrates a particular bus, this
disclosure contemplates any suitable bus or interconnect.
Herein, a computer-readable non-transitory storage medium or media
may include one or more semiconductor-based or other types of
integrated circuits (ICs) (such, as for example, field-programmable
gate arrays (FPGAs) or application-specific ICs (ASICs)), hard disk
drives (HDDs), hybrid hard drives (HHDs), optical discs, optical
disc drives (ODDs), magneto-optical discs, magneto-optical drives,
floppy diskettes, floppy disk drives (FDDs), magnetic tapes,
solid-state drives (SSDs), RAM-drives, SECURE DIGITAL cards or
drives, any other suitable computer-readable non-transitory storage
media, or any suitable combination of two or more of these, where
appropriate. A computer-readable non-transitory storage medium may
be volatile, non-volatile, or a combination of volatile and
non-volatile, where appropriate.
Herein, "or" is inclusive and not exclusive, unless expressly
indicated otherwise or indicated otherwise by context. Therefore,
herein, "A or B" means "A, B, or both," unless expressly indicated
otherwise or indicated otherwise by context. Moreover, "and" is
both joint and several, unless expressly indicated otherwise or
indicated otherwise by context. Therefore, herein, "A and B" means
"A and B, jointly or severally," unless expressly indicated
otherwise or indicated otherwise by context.
The scope of this disclosure encompasses all changes,
substitutions, variations, alterations, and modifications to the
example embodiments described or illustrated herein that a person
having ordinary skill in the art would comprehend. The scope of
this disclosure is not limited to the example embodiments described
or illustrated herein. Moreover, although this disclosure describes
and illustrates respective embodiments herein as including
particular components, elements, feature, functions, operations, or
steps, any of these embodiments may include any combination or
permutation of any of the components, elements, features,
functions, operations, or steps described or illustrated anywhere
herein that a person having ordinary skill in the art would
comprehend. Furthermore, reference in the appended claims to an
apparatus or system or a component of an apparatus or system being
adapted to, arranged to, capable of, configured to, enabled to,
operable to, or operative to perform a particular function
encompasses that apparatus, system, component, whether or not it or
that particular function is activated, turned on, or unlocked, as
long as that apparatus, system, or component is so adapted,
arranged, capable, configured, enabled, operable, or operative.
Additionally, although this disclosure describes or illustrates
particular embodiments as providing particular advantages,
particular embodiments may provide none, some, or all of these
advantages.
* * * * *